Circuit interrupter



April 18, 1950 J. R. MCFARLIN cmcun" INTERRUPTER 2 Sheets-Sheet 1 Filed July 19, 1944 I I 1 r x April 18, 1950 J. R. MCFARLIN CIRCUIT INTERRUPTER 2 Sheets-Sheet 2 Filed July 19, 1944 A Q I INV rial in fihi/VQZE? \r/ .fl orl-aey Patented A r. is, 1950 CIRCUIT IN TERRUPTEB John Robert McFarlin, Philadelphia, Pa., aosignor to Electric Service Manufacturing Company, Philadelphia, Pa., a corporation of Pennsylvania Application July 19, 1944, Serial No. 545,848

3 Claims. (Cl. 200-115) My invention is a circuit interrupter or electrical disconnector primarily designed for use in conjunction with a lightning arrester and with a line circuit breaker or fuse so coordinated with the disconnector that the latter will not be affected by discharges passing through a properly working arrester but will be opened by discharges passing through a defective arrester to isolate such defective arrester and prevent the opening of the line circuit breaker or fuse.

Lightning arresters are usually connected in shunt around the insulation of the equipment or line they are designed to protect,'as, for example, between terminals of a transformer, between a terminal and tank, between a terminal and earth, or between a circuit conductor and earth. The arc gaps of an arrester in good working order normally prevent the initiation of flow of normal dynamic current through the arrester to ground, and when dynamic current follows a discharge of lightning or surge current to ground the arcs maintained across the gaps by the dynamic current are extinguished by the action of a characteristic element to check the dynamic current flow before it can actuate a circuit breaker or blow a line fuse.

When, however, a lightning arrester protecting a circuit fails, the dynamic current flow continues and generally a line circuit breaker is operated or a line fuse is blown: with resulting outage of the circuit until the defective arrester is located and removed.

My invention provides a disconnector which will automatically disconnect a failed arrester from ground or line, will prevent the outage of a *circuit due to failure, and will visualljiindicate the failed arrester.

In accordance with my invention, the operation of the disconnector is controlled, responsively to dynamic current flow therethrough, by an are having an arc voltage and current flow sufficient to operatively affect a thermally responsive element in a period of time less than that required for the actuation of the line circuit breaker or fuse by a flow to ground of substantially less than the full short circuit discharge under the particular operating conditions of a particular circuit. The energy of the arc transmitted to the thermally responsive element is insufficient to operatively affect the thermally responsive element within the period of time normally required for the extinction of the are by a properly operating lightning arrester in series and coordinated therewith, or even within a half cycle of the dynamic current.

The are is formed between fixed gap electrodes whose positions are unaffected by the operation of the disconnector and the energy of such arc is preferably utilized to fuse a fusible bond in close proximity to the arc and thereby release and permit the ejection of a conductor forming part of the arrester shunt circuit to ground. The are is initiated between the spaced gap electrodes of the disconnector by a discharge of abnormal surge current or lightning whose duration or amount is insuiilcient to effect the fusion of the bond. The follow current is normally interrupted by the arrester before sufficient are energy is produced to fuse the bond. Upon failure of an arrester, the magnitude of follow current flow is generally insufficient to effect instantaneous (within a half cycle) operation of a circuit cutout but is sufficient to effect fusion of the disconnector bond within a time less than that required for the operation of the line circuit breaker or fuse, whose time lag is proportioned inversely to the magnitude of current flowing therethrough.

The characteristic features and advantages of my invention will further appear from the following description and the accompanying drawings in illustration thereof:

In the drawings, Fig. 1 is a longitudinal sectlol a1 view illustrating a preferred form of my 8191 trical disconnector mounted in the base of a ligljming arrester; Fig. 2 is a transverse sectional view taken on the line 2-4 of Fig. i; Fig. 3 shows the electrical disconnector of Figs. 1 and 2 on a smaller scale and mounted in complementary relation to a complete lightning arrester; Fig. 4 is a longitudinalsectional view showing a modified form of my electrical disconnector threaded on the ground stud of a lightning arrester; Fig. 5 shows a further modified form of my disconnector connected with the ground line of a lightning arrester; Fig. 6 is a longitudinal sectional view showing a further modification of my electrical disconnector mounted on a ground line of a lightning arrester; and Fig. '7 is an external view of the electrical disconnector of Fig. 6 coupled to the ground terminal of a lightning arrester.

In the embodiment of my invention illustrated in Figs. 1, 2 and 3, my improved electrical disconnecto comprises the air-spaced arc gap electrodes I and 2 and conductor 3 having its end anchored in a socket I of the electrode 2 by a thermally responsive bond, such as the lowmelting-point solder 5. A sleeve 6 is fixed to the conductor 3 and has a shoulder I for supporting 3 an apertured cup-like spring retainer I in spaced relation to the electrode 2. A coiled spring 9 encircles the conductor 3 and sleeve 8 and is compressed against the retainer 8 by a slotted plate l0, which is detachably engaged in a peripheral groove II in the electrode 2.

The parts 2 to In may be pre-assembled as a unit and then positioned in cooperative relation with the electrode I; the faces of the electrodes being spaced a predetermined distance by the interposition of the insulating annular spacer I2 between the electrode i and the plate It. The plate I is held against the spacer i2 by the annular insulating spacers l3 and I4, which rest on a split spring ring l5 expanded in the groove IS in the inner surface of a tubular housing II. The tubular housing I1 is permanently held in fixed relation to the electrode l by a sealing compound and cement l9 solidified in the bottom of the casing 20 of a lighting arrester of the gencral type illustrated in my Letters Patent Nos. 1,763,667 and 2,150,167.

The conductor 3 is normally connected ground, or the equivalent thereof, and the flow of current to the electrode l is controlled by the characteristic element 2! of discrete silicon carbide and by the gap electrodes 22 in series with it. The conductor 23 of the arrester 20 is connected with a "line or source of current.

The body of discrete silicon carbide 2i has an inverse resistance voltage characteristic interposing little resistance to the discharge of high potential surges but offering high resistivity to the passage of dynamic current.

Should the element 2| for any reason fail to interrupt a follow flow of dynamic current, with consequent maintenance thereby of an arc initlated by surge current between the air-spaced gap electrodes I and 2, the heat generated by such arc is transmitted by thermal conductance through the metallic electrode 2 to the low-melting-point solder 5. The close thermal proximity of the solder 5 to the arc causes a softening or melting of the solder in a time varying with the heat of the arc, which varies with the resistance of the arc and the square of the current flow.

When the duration and intensity of the arc reduces the holding power of the solder below the expansive force of the spring 9, the latter expands and expels the conductor from the electrode 2 and housing i1, thereby definitely interrupting the flow of dynamic current to ground.

Normally the disconnector will be operated only upon the failure of the arrester, since they are so designed that they will withstand, without operating, the maximum lighting or surge current that can be safely carried by the lightning arrester. Tolerances permissible and necessary in the manufacture of disconnectors may, however, affect their operating characteristics, including their ability to carry lightning or surge current; likewise tolerances permissible and necessary in the manufacture of lightning arresters may affect their operating characteristics, including their ability to carry lightning or surge currents; and, as is well known, the characteristics of lightning and surge currents discharged into lightning arresters from the circuits to which they are connected vary widely as to voltage, current, wave shape and duration.

It may therefore be expected that with even the most highly developed type of disconnector, conditions in service may occasionally occur where the disconnector may operate under lightning conditions not severe enough to damage the lightning arrester of which it is a part. Should improper operation of the disconnectc occur, due, for example, to initially defective anchoring of conductor 3 in socket 4, or to ageing or crystallization of the thermally-responsive bond 5, even though initially properly applied,

.the disconnector may readily be disassembled by extracting the retainer I! from its groove II and removing the parts positioned thereby to permit inspection of the end of conductor 3 and of the arcing surface of electrode 2. Improper operation of the disconnector will be clearly indicated by absence of severe arc burns on the end of conductor'3 and on the arcing surface of electrode 2. Under such conditions a new assembly consisting of electrode 2, conductor 3 and sleeve 6 may be re-assembled in tube II as above described. The ability to readily disassemble my disconnector, inspect internal parts, determine whether or not the lightning arrester itself has been damaged and, if not damaged, to re-assemble the unit and put it back into service again in such cases as the foregoing, overcomes the possibility of discarding an otherwise operative arrester, with consequent economics incident thereto.

As illustrated in Fig. 4, the unit assembly comprising the parts 2 and ill, inclusive, and the spacer l2 may be assembled in an insulating tubular housing i1 having a shoulder 24 for supporting the plate iii. A threaded metal cap has a threaded flange 25 screwed on the exteriorly threaded top of the tube ll, a disk portion 28 forming an electrode in air-spaced relation to the electrode 2, and an interiorly threaded socket 21 adapted for receiving a conventional threaded ground stud 28 of a lightning arrester, such as shown in Fig. 3 or in my patents above referred to.

Should an arc of sufficient intensity and duration to melt the solder 5 be maintained across the air space between the gap electrodes 2 and 28, the expansion of the spring 9 expels the conductor 3 and interrupts the flow of dynamic current to ground. Thereafter the housing l1 may be unscrewed from the cap flange 25 to afford access to the electrodes 2 and 26 and the determination from their condition whether the arrester has failed and should be removed or whether the disconnector parts may be safely reassembled or replaced.

In the embodiment of my invention illustrated in Fig. 5, the bottom plate or electrode l of a lightning arrester, similar to that shown in Fig. 3. is connected through a conductor 29 with a tapered electrode 30 having a threaded shoulder 3| screwed into an insulating tubular housing 32 and locked therein by suitable means, such as the member 33. The electrode 30 is air-spaced by an insulating annular spacer 34 from an electrode 35, which rests on a shoulder 36 in the housing 32. The electrode 35 contains a socket in which is soldered a. flanged sleeve 31 in which the conductor 3 may be secured by crimping the socket wall or by soldering. A coiled spring 38 encircles the sleeve 31 between its bottom flange and the bottom of the electrode 35. When an arc of suiilcient intensity and duration between the electrodes 30 and 35 melts the low-melting-point solder 5, the spring 38 expands to expel the sleeve 31 and conductor 3. Access to the electrodes 30 and 35, to determine from the condition thereof whether the arrester has failed, may be readily had by removing the member 33 and unscrewing the tubular housing 32 from the shoulder 3|.

In the embodiment of my invention illustrated in Figs. 6 and 7, an electrode 40 is crimped ,on the end of a conductor 4| and positioned in an insulating housing 42 by a disk 43 clamped by an insulated threaded cap 44 against a, washer 45 on the end of the housing 42. The disk 43 is preferably made integral with the electrode 40 or may be rigidly secured thereto by soldering, crimping or the like. An electrode 46, complementary to and air-spaced from the electrode 40, is inserted in the opposite end of the housing 42 and supported by the flanged conoidal shell 41 having its outer flange gripped between the threaded cap 48 and the end of the housing 42 on which the cap 48 is screwed. The electrode 46 contains a socket in which a conducting sleeve 49 is anchored by the low-melting-point solder 5. The sleeve 49 is crimped on the end of a ound conductor 3 and has a shoulder supporting a spring retainer 50. A compressed coiled spring 5| encircles the sleeve 49 between the retainer 50 and the inner flange of the shell 41.

As shown in Fig. 6, the conductor 4| may be connected directl with the bottom plate or electrode of a lightning arrester, such as shown in Fig. 3, or, as shown in Fig. 7, the conductor 4| may be detachably connected by a coupling bolt and nut 52 and 53 with a conductor or ground boss 54 connected with an electrode When an arc of suflicient intensity and duration to melt the solder 5 is maintained between the electrodes 40 and 46, the spring 5| expels the sleeve 49 and conductor 3 so as to interrupt the discharge path to ground. The access to the electrodes 40 and 46 may be readily had by unscrewing the cap 48,

The dangling conductor 3 afiords, in each instance, a visual indication that investigation of the condition or the arrester is required, and the readily accessible electrodes of the disconnectors afford convenient means for making a preliminary investigation of such condition.

The dlsconnector interposes a substantially lower impedance to the discharge of surge currents than the impedance or the arrester to such surge currents, since the disconnectors gap elements' are made of metal, e. g. copper, brass, or sliver, of high electrical, as well as thermal, conductivity and the arc space between them is only wide enough to permit formation of a heating are and not to substantially impede the flow of either surge or dynamic current.

The gap electrodes of the dlsconnector are not disturbed or exposed by the expulsion of the conductor element and hence provide reliable indlcia as to whether the master has actually failed 6 long after the expulsion of the conductor element. and the electrodes themselves are seldom lost or need replacement.

Having described my invention, I claim:

1. In an electrical disconnector, an assembly comprising a member containing a socket, a conductor anchored in said socket by a fusible material, a spring retainer fixed to said conductor in spaced relation to said member, a spring surrounding said conductor and member and bearing against said retainer, and a detachable bearing mounted on said member between the ends thereof for compressing said spring, said bearing containing a slot extending from its periphery toward its center and permitting its positioning on and removal from said member.

2. In an electrical disconnector, a member containing a socket, a conductor anchored in said socket, thermally responsive means, a spring retainer fixedly connected with said conductor in spaced relation to said member, a spring en- Circling said conductor and member and bearing against said retainer, a radially slotted plate mounted on said member and compressing said spring, a housing, and spacers within said housing and engaging said plate for positioning said member therein.

3. A disconnector comprising an insulating grooved housing, air-spaced arc electrodes in said housing, an expansion ring complementary to the groove in said housing for positioning one of said electrodes relatively to the other, a conductor connected with one of said electrodes, and thermally responsive means affected by an are between said electrodes for releasing said conductor from said electrode without disturbing the relative position of said electrodes.

JOHN ROBERT McFARLIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,352,117 Davis Sept. 7, 1920 2,174,477 Pittman et al Sept. 26, 1939 2,276,054 Ludwig Mar. 10, 1942 2,279,051 Maerkisch Apr. 7, 1942 2,286,534 Goldner June 16, 1942 2,296,708 Earle Sept. 22, 1942 2,305,436 McMorris Dec. 15, 1942 2,315,320 Earle Mar. 30, 1943 2,374,560 Nelson Apr. 24, 1945 OTHER REFERENCES Crystal Valve Lightning Arresters," catalog #390 of Electric Service Supplies 00., May 15, 1937, page 23, col. 2. 

